The present invention relates to a new and improved thin absorbent structure, and more particularly, to a new and improved compressed absorbent composite containing superabsorbent material, and which composite absorbs large quantities of liquids.
Disposable absorbent products have been known for some time including such products as disposable diapers, sanitary napkins, wound dressings, bandages, incontinent pads, and the like. These products incorporate an absorbent batt which is used to absorb and hold, or contain, body fluids. Initially, in many of these products, especially diapers and sanitary napkins, the absorbent batt consisted of what is termed "wadding" or plies of tissue. The wadding was disposed between an impermeable backing and a permeable facing and the plies of tissue were used to absorb and hopefully contain the liquid within the product. A diaper which utilizes such an absorbent batt is disclosed in U.S. Pat. No. Re. 26,151.
The wadding type of batt was replaced for the most part by an improved absorbent batt which comprises what is termed "fluffed wood pulp fibers". This absorbent batt comprises a layer of individualized wood pulp fibers with the layer having substantial thickness. A diaper which incorporates such a fluffed wood pulp absorbent batt is described in U.S. Pat. No. 2,788,003. This diaper had improved absorbent capacity and somewhat better containment than a diaper using a wadding layer. Also, the fluffed wood pulp layer is quite soft, flexible, and conformable, and hence produces an improved diaper over diapers using wadding as the absorbent layer.
Though the fluffed wood pulp absorbent batts have improved capacity, the efficiency with which the capacity is used in a diaper or sanitary napkin is poor. The reason for this is that the fluid to be absorbed is generally deposited in a localized area within the absorbent batt and the ability for the fluid to move along the plane of the batt is poor. The fluid follows the path of least resistance, and consequently moves to the closest edge of the batt where it generally is no longer contained and the product leaks. Furthermore, the wood pulp batts lack stability, e.g., when a diaper is being worn, the batt tends to break up creating bunching.
U.S. Pat. No. 3,017,304 discloses an absorbent product which incorporates a fluffed wood pulp absorbent batt having a densified paper-like layer. This paper-like layer acts as a wick, i.e., liquid which is placed on the layer tends to move rapidly along the plane of the layer. When incorporated in combination with fluffed wood pulp fibers, the resultant product uses the absorbent capacity of the fluffed wood pulp much more efficiently. Diapers which incorporate this paper-like layer combined with fluffed wood pulp are disclosed and described in U.S. Pat. Nos. 3,612,055 and 3,938,522. This concept of combining a wicking layer or capillary skin with fluffed wood pulp fibers has gained wide acceptance in many absorbent products including disposable diapers and sanitary napkins. Even though these products make much greater use of the capacity of the absorbent batt, they still do not totally contain the absorbed liquid. It is probable that these products will leak before the full capacity of the batt is used for absorption. This is especially true if pressure is placed on the batt while wet. For example, a baby sitting down on a previously wetted diaper will very often cause the batt to leak. Although the batt is somewhat stabilized by the paper-like densified skin, it may crack and separate.
A number of years ago "superabsorbent materials", i.e., materials which will absorb many times their weight of liquid, were developed. Since the development of such materials, people have been trying to incorporate them in absorbent products such as diapers and sanitary napkins to enhance the absorptive performance of these products. Theoretically, a minimum amount of superabsorbent incorporated in a product would make that product perform as well or better than the prior art products. Perhaps one of the first products to incorporate such a superabsorbent material in a disposable diaper is disclosed in U.S. Pat. No. 3,670,731. This patent discloses an absorbent dressing comprising an absorbent layer sandwiched between a permeable facing and an impermeable backing sheet. The absorbent layer contains water insoluble, crosslinked, hydrocolloid polymer as the absorbent material.
Even though absorbent materials have been available for some time, they have not gained wide acceptance in absorbent products such as disposable diapers and sanitary napkins. A primary reason for this lack of acceptance of the superabsorbents is failure to develop a product capable of economically utilizing the highly increased absorptive capacity of the superabsorbent material. In order to economically utilize the superabsorbent, the liquid being absorbed must be transported to the superabsorbent material. In other words, the superabsorbent material must be placed in contact with the liquid.
Furthemore, as the superabsorbent material absorbs the liquid, it must be allowed to swell. If the superabsorbent is prevented from swelling, it will cease absorbing liquid. Hence, if the superabsorbent material is to function in diapers and sanitary napkins wherein the liquid to be absorbed is placed in a small void area, the structure of the absorbing layer containing superabsorbent material appears to be critical. Over the years, a number of techniques have been disclosed in an attempt to provide structures which make efficient use of the superabsorbent material, such products are disclosed in U.S. Pat. Nos. 4,103,062; 4,102,340; and 4,235,237. In addition, methods for incorporating superabsorbents into suitable layers or suitable configurations which can be placed in an absorbent product are disclosed in U.S. Pat. Nos. 4,186,165; 4,340,057; and 4,364,992. To date, none of these products has met with any substantial commercial success.
In an attempt to overcome these problems, in copending application Ser. No. 439,963 filed Nov. 8, 1982, a particularly useful compressed composite structure is formed. Application Ser. No. 439,963 is hereby incorporated by reference. The compressed composite is a layered structure which contains an absorbing layer, a wicking layer and a transition zone. The product is compressed. The absorbing layer is generally a high loft, nonwoven, fabric such as polyester, which layer contains at least 200 percent superabsorbent. Although this layer potentially has high liquid absorption capability, it is necessary to provide a transporting mechanism so that liquid which is deposited locally on the superabsorbentcontaining web can be transported. In order to provide this, a wicking layer is placed on the absorbing layer and the two layers are compressed, thus providing a transition zone at the contact point of the two layers. The wicking layer generally is a wood pulp fiber layer. Although the resulting compressed composite readily accepts, transports, and absorbs liquid, the product is somewhat stiff, and hence requires softening to provide flexibility for utilization in products such as diapers and the like. The flexibility provided needs to be permanent, i.e., the surrounding environment, handling of the product, and its subsequent use will not affect the softness and flexibility.
The present invention provides a new and improved absorbent composite structure which utilizes a substantial portion of the absorptive capacity of superabsorbent materials and yet is reasonably soft and flexible. This composite remains in its substantially, completely, stable state, though rendered soft and flexible. Whether wet or dry the composite does not break, bunch, or separate. Furthermore, the composite retains absorbed liquid without yielding any of the liquid when the composite is under pressure.